1. Technical Field
Embodiments of this invention relate to a method for corrosion assessment. Embodiments of this invention relate to a system for implementing a method of corrosion assessment.
2. Discussion of Art
Petroleum may be obtained as crude oil, and may contain a complex mix of components. One type of component is a naphthenic acid or naphthenic acid precursor. The presence of naphthenic acid or naphthenic acid precursor can affect the corrosion potential of the crude oil.
Crude oil is “sweet” if it contains less than 0.5% sulfur, compared to a higher level of sulfur in sour crude oil. Sweet crude oil may contain a small amount of hydrogen sulfide and carbon dioxide. High quality, low sulfur crude oil may be processing into gasoline and is in high demand. “Light sweet crude oil” is a most sought-after version of crude oil as it contains a disproportionately large amount of these fractions that are used to process gasoline, kerosene, and high-quality diesel. Sour crude oil contains impurities such as hydrogen sulfide, carbon dioxide, or mercaptans. While all crude oil contains some impurities, if the total sulfide level in the oil is >0.5% the crude oil is called “sour”. The term “opportunity crude oil” refers to crude oil that is of non-standard origin or is from a field that is of unknown or varying quality or composition. The presence of sulfur and sulfur compositions can affect the corrosion potential of the crude oil.
Corrosion may be problematic in petroleum refining operations of crude oils. Corrosion in atmospheric and vacuum distillation units at temperatures greater than about 200 degrees Celsius may be of concern. Some corrosion may be associated with corrosive species, such as those disclosed above. Factors that contribute to the corrosivity or corrosion potential of crude oil that contains corrosive species include the amount of naphthenic acid present, the molecular structure of the naphthenic acid precursor, the concentration of sulfur compositions, the total availability of the acids, the velocity and turbulence of the flow stream in the units, and the like.
High temperature corrosion control attempts have included blending a higher naphthenic acid content crude oil with a relatively low naphthenic acid content crude oil; neutralizing or removing naphthenic acid precursors from the crude oils; and use of corrosion inhibitors. Corrosion inhibition of the inward-facing metallic surfaces of refinery equipment has been attempted by adding an additive to the crude oil. The additives known so far include a phosphate composition containing at least one aryl group, and a mercaptotriazine composition.
Refineries monitor the corrosion by placing corrosion monitoring devices in locations throughout the refineries. Unfortunately, identifying suitable monitoring locations is a challenge as the identified spots should be representative of the corrosion level of the entire system. That is, the corrosion monitoring devices only see a small patch of area within a large piping network, and cannot extrapolate that data to represent non-monitored areas. Without information on the general corrosion state, or the specific corrosion state in non-monitored areas, choosing an appropriate treatment response may be problematic. The treatment response may include variables such as dosage type, amount, frequency, and location for addition. Without informational guidance, the treatment response may not be as effective as is possible or desirable.
A further complicating factor is a lack of an adequate corrosion model for naphthenic acid precursors and sulfur compositions corrosion factors. Without an adequate model, the various naphthenic acid precursors and sulfur compositions are treated equally—despite their actual behavior showing they do not contribute equally to corrosion. The necessary but inadequate presumption that all naphthenic acid components and sulfur compositions have the same corrosive tendency has led to discrepancies in treatments and actions taken at crude oil refineries.
There may be a need for a method of assessing corrosion that differs from those methods currently available. There may be a need for a system capable of assessing corrosion that differs from those systems that are currently available.